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  Method and an apparatus for shape measurement, and a frequency comb light generatorUSPTO Application #: 20080018906Title: Method and an apparatus for shape measurement, and a frequency comb light generator Abstract: This apparatus for shape measurement comprises a frequency COMB light generator and an optical interferometer for measuring the distance. The frequency COMB light generator includes a laser light source 11, an optical resonator 13, a COMB pitch regulator 14 and an output port OUT. The optical resonator 13 includes an optical modulator 131, a first mirror M11, an optical fiber F13 which is drawn out from alight waveguide of the optical modulator. The COMB pitch regulator 14 is a modulation signal generator for varying the modulation signal. The optical fiber F13 is equipped with an apparatus (Faraday rotation mirror) for compensating a change in the polarization condition.
A method and an apparatus for shape measurement that is able to observe the deep portion under a skin with high spatial resolution by using a frequency COMB light generator is provided. A frequency COMB light generator for generating multiple frequency COMBs with variable frequency pitch at high operation stability is provided. (end of abstract)
Agent: Kanesaka Berner And Partners LLP - Alexandria, VA, US Inventors: Takashi Kurokawa, Yousuke Tanaka, Tatsutoshi Shiota USPTO Applicaton #: 20080018906 - Class: 356479000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080018906. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This invention relates to a method and an apparatus for shape measurement that is able to observe the deep portion under a skin with high spatial resolution by using a frequency COMB light generator. This invention also relates to a frequency COMB light generator for generating multiple frequency COMBs with variable frequency pitch at high operation stability. BACKGROUND ART [0002] The Optical Coherence Tomography (OCT) is known for obtaining a tomogram of the structure under a skin by applying the light through a living body skin and detecting the reflected light from an internal anatomy) See Japanese Patent Application Laid-Open No. 2004-191114). [0003] FIG. 11(A) shows a prior art an optical coherence tomography system. In FIG. 11(A), an optical coherence tomography system 8 includes a low coherence light source 81, a condensing lens 82, a half-mirror 83, a reference mirror 84, an actuator for moving the reference mirror 85, an object lens 86, a detecting lens 87, a light detector 88 and a control computer 89. [0004] The elements of the optical coherence tomography system 8 excepting the low coherence light source 81 and the computer 89 constitutes an optical interferometer. A light source with a wide spectrum width like LED, SLD (Super Luminescent Diode), etc. is used as the low coherence light source 81 and has a spread wave length spectrum (e.g. tens nm or wider) as shown in FIG. 11(B). [0005] The low coherence light source 81 is controlled by a control signal A1 from the computer 89. The light from the low coherence light source 81 is collimated by the condensing lens 82 and is output to the half mirror 83. The half-mirror 83 splits the light from the condensing lens 82 into two parts, directs one part to the reference mirror 84 and directs the other part to a measured object O through the object lens 86. [0006] The half-mirror 83 also combines the reflected light from the reference mirror 84 with the reflected light from a reflection point within the measured object O and outputs the combined light to the light detector 88 through the detecting lens 87. [0007] The reflected light from the measured object O includes the light reflected at the surface, the light reflected at a shallow internal point and the light reflected at a deep internal point. [0008] Since the light uses for detection is a low coherence light, the reflected light which experienced an interference includes only the reflected light from the plane at the position where the distance form the half-mirror 83 is (L.sub.0.+-.L.sub.0'/2), where L.sub.0 is the distance between the half-mirror 83 and the reference 84 and L.sub.0' is the coherence length. [0009] By changing the distance between the half-mirror 83 and the reference 84 by the actuator 85 (controlled by a control signal A2 from the computer 89) it is possible to selectively detect only the reflected light from the reflection plane that corresponds to the distance. [0010] By this technique it is possible to calculate the reflection index at any position inside the measured object O by the computer 89 and provide the visual internal structure information for the measured object O by displaying the distribution of the calculated reflection index onto a display screen (not shown). DISCLOSURE OF INVENTION [0011] The output of the low coherence light source 81 in FIG. 11(A) has a wide spectrum width as mentioned above (See FIG. 11(B)). Although the spatial resolution in the depth direction is high in the optical coherence tomography 8, the deep portion inside the measured object O cannot be observed because the light intensity is low and the output level is very low due to the low efficiency. Furthermore the observation by this system is time consuming and the creditability is not necessarily high because the reference mirror is movable. [0012] It has been studying to improve the spatial resolution by using a femto-second laser with a wide spectrum width as a light source of an optical coherence tomography system. However, this type of optical coherence tomography system becomes big and expensive, and therefore it is not suitable for usage in clinics. [0013] A technique for synthesizing a hypothetical frequency COMB light as a time average like a coherence function synthesizing method is known. However the application of this technique is limited to distance measurement like a fiber-sensing because the frequency pitch cannot be shortened and the number of generated COMBs is limited (See Japanese Patent Application Laid-Open No. 10-148596) and therefore this technique is not suitable for shape measurement like observation of the anatomy under a living body skin. [0014] A prior art frequency COMB light generator 9 shown in FIG. 12(A) includes a laser light source 91 and an optical resonator 92. The optical resonator 92 includes an optical modulator 922 formed on a LN(LiNbO.sub.3) substrate 921 and mirrors M01, M02. The output signal (angular frequency .omega..sub.0) of a laser light source 91 is modulated and frequency shifted by a modulation signal RF0 in the optical resonator 92, and then repeatedly reflected by the mirrors M01, M02 and repeatedly modulated, The optical resonator 92 outputs the laser light (modulated light ML) shown in the drawing. [0015] This modulated light ML is shown in FIG. 12(A) as a frequency component FE and includes discretely multiple frequency components as shown in FIG. 12(B). As shown in these drawings, the center of angular frequencies is at .omega..sub.0 and the distribution of the angular frequencies has a higher frequency side band and a lower frequency side band. [0016] However it was difficult to make the frequency pitch of the frequency COMBs variable because the frequency pitch of the frequency COMBs is determined by the distance between mirrors M01 and M02 in the frequency COMB light generator 9. [0017] A purpose of the present invention is to provide a method and an apparatus like an optical coherence tomography system for observing the anatomy under a living body skin with a high depth spatial resolution to a deep position by using a frequency COMB light generator which is capable of changing the frequency pitch of the frequency COMBs as an optical source. [0018] Another purpose of the present invention is to provide a frequency COMB light generator which is capable of operation with high stability, variable frequency pitch of frequency COMBs and generation of multiple frequency COMBs by using a simple configuration. BRIEF DESCRIPTION OF DRAWINGS [0019] FIG. 1 is shows a first embodiment of a frequency COMB light generator according to the present invention. [0020] FIG. 2 (A) shows a first example of an optical modulator in the frequency COMB light generator shown in FIG. 1; (B) shows a perspective view of the optical modulator shown in (A); (C) shows a spectrum of the output light from the optical modulator shown in (A) and (B). Continue reading... Full patent description for Method and an apparatus for shape measurement, and a frequency comb light generator Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and an apparatus for shape measurement, and a frequency comb light generator patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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